The present invention relates to a load-cell balance making use of strain gauges.
Generally, the load-cell balance of the kind described has a beam or frame provided with four thin-walled flexible portions adapted to be deflected by an application of a load and four strain gauges adhered to respective flexible portions, the strain gauges being connected in the form of a bridge so that the load is picked up as an electric signal. In order to check the influence of external conditions, it is necessary to take necessary measures to protect the strain gauge against moisture. This moisture-proofness is realized in various manners.
Firstly, it has been a practical measure to effect a seal by means of a metallic bellows or the like. This type of structure, however, impractically limits the usable shape of construction and is expensive, although it can provide a good seal against moisture.
Secondly, it has been adopted to form a coating with a moisture proof material such as silicon rubber. This structure, however, cannot provide a good sealing effect due to a poor sealing nature of the material.
The third way is to form a coating with a moisture proof sealant of the epoxy group. This sealant forms a good seal against the moisture but cannot be successfully used for a balance of small capacity, because the sealant is hardened to adversely affect the load-cell characteristic such as creep or hysteresis, resulting in a deteriorated precision of measurement.